The first and at one time largest of the microstock libraries. Now part of the Getty images empire. Since 2003 we have watched the cost of photos steadily rise (good news for photographers), gone are the days when you could get a good usable image for $1, they introduced XSmall images and in effect the cost of an image tripled overnight. In early 2010 exclusive images doubled in price making istockphoto very attractive to those who are willing to tie their images to just one agency.
Overall the site is still popular among buyers having an almost cult following, if difficult to get images accepted; you should include iStockPhoto in your portfolio. Don't lose any sleep if as a non exclusive you earn less on this site than on some of the other smaller sites. I have seen reasonable returns throughout last year (2011) despite changes search that place non exclusives like me at a serious disadvantage
The Killer Search

From all the work that goes into disambiguation of uploads istockphoto should have pretty much the best search technology ever seen at a microstock agency. Sadly as of 2011 the implementation leaves a lot to be disired and it's clear that some other financial or business concerns are seriously eroding the quality of search results. The search tecchnology used It makes it slightly more difficult to upload to as you have clarify the meaning of your keywords. for example include a keyword 'orange' and you will be asked to tick one of two boxes Orange (Descriptive Colour) or Orange (Citrus Fruit), or perhaps you include the keyword 'lead' the response will be Lead (Metal), Dog Lead (Pet Equipment), Leading (Moving Activity), Graphite (Material) etc and the list goes on for 1000's of different ambiguous words in the English language. This really is cool stuff, as an image purchaser trying to clarify exactly what sort of image you want using words is a difficult business and this helps significantly.
Exclusive Photographer? 
A big decision for any photographer to make. Becoming exclusive with istock will mean that you cannot upload images to any other site. I can't comment on what its like to be exclusive as i have no experience, many people swear by it. exclusive photographers get a larger percentage per image purchase, and also receive 'care' from the site - istock will chase people who use your images in breach of the license on your behalf. You will also come across 'Exclusive+' which allows exclusive photographers to nominate a small ammount of their images for sale at a higher price.
The top exclusive photographers also get to sell their images via getty's image network (including photodisk) increasing sales potential dramatically.
Audio, Video, Ilustration, Music, Flash, Logos... 
Along with several other agencies istockphoto also accept video and vector illustrations. They have recently launched their new audio library 'istockaudio'. Even if you only contribute photographs to istock it's important to consider that buyers may find istock a convenient one-stop-shop for all their media needs, and these buyers will be your potential customers.
It's true that at present many buyers are only in the market for images, but demand for video is growing fast and commission rates are higher. I can see one recipe for success in this emerging market is having quality video with matching print resolution images, hence designers can create matching online video and web/print campaigns; perhaps even just the option to go back and download matching images if they become needed will be enough to make your video work stand out.
istock Tips 
Uploading
Istock is the only major microstock site that does not support FTP/SFTP upload. There are a couple of work-arounds for this. Firstly there is the istock image manager available for download from their site (istockphoto.com/ws_client_intro.php). The second option is to use picworkflow or similar upload assistant to submit images but make sure you log into istockphoto and set those categories and keywords once the upload is done. The third option is a simple time saver: bookmark the page that is shown when you have clicked “upload > image type” (the one with a browse button) put the bookmark in a shortcut bar in your browser, then once you have logged in you can click it and save yourself a couple of clicks and page loads for every image you want to upload i.e. just click that shortcut when you receive the upload confirmation page and you are ready for another image.
Promotion
I stock has a several useful features you can use to increase your sales. First up you can embed simple html into your image descriptions, these can be used to direct potential buyers to other images that you have uploaded that match the image, i.e. those in the same series or of a matching theme. You could also create a small banner for a public lightbox and link to that from the image description (that way the code is the same for each of the related images). You can see in the example below the photographer has linked to several related images in the description:
Another useful promotion tip is to either create a couple of ‘visual blog posts’ in your personal istock blog that link to either a lightbox or some recent images. Other similar options might just be including thumbnails to a select number of your favorites. Either the blog tab or the profile tab (if you have not created any blog posts) is displayed to visitors when they arrive on your profile page – this is the place to sell yourself. Buyers are interested in the quality (both technical and artistic) and choice of images you have, try to emphasize those as key selling points.
Conclusion
Despite my criticisms of this site, the low commission level (recently dropped to 15% for non exclusives, compared to previous levels of about 28% - note: commissions increase with sales), restrictions on the number of images that can be submitted (for full time microstockers istock is quite restrictive) the fact that it has fallen from the #1 spot, tedious keywording process etc, I still recommend istockphoto as one of the top four earning microstock agencies. The microstock market moves and changes all the time.
August 2010: I stock announce that they payout over 1.7 million dollars every week to their contributing artists.
(as It appears I will take a pay cut of upto 50-70% at istockphoto this year, 2012 will be somewhat of a watershead, but I'm not making any judgements until the results are in.)




is it still possible for amateurs to join?
Ronnie Hall (not verified) on Tue, 11/10/2009 - 11:26Certainly not a top 10 agency
Jab (not verified) on Sat, 11/13/2010 - 16:58Not quite sure how this
Steve Gibson on Sun, 11/14/2010 - 23:59Not quite sure how this comment fits into the middle of the thread about joining, but with the sales figures as they are there is no way, no matter how much you dislike it, that it is not a top 5. They definitely belong up there, measured on sales, images, contributors and any other metric I can think of - including photographer ire.
I have to side with you on the issues after F5, it's was all decidedly shaky with broken links, ophaned pages etc, and dodgy search for several days most of that is sorted now?
no website that big is ever perfect, especially in those dark corners. Poor interface? - well Controlled vocab often gets peoples back up because, well, yes it's tedious at first until you learn the way it works. (personally I didn't like the new search at all).
Joining
Steve Gibson on Wed, 11/11/2009 - 01:58Bad
Henri Faure (not verified) on Tue, 11/17/2009 - 13:04don't don't
Steve Gibson on Wed, 11/18/2009 - 02:47Exclusive Contributors
Alistair Shankie (not verified) on Sun, 01/10/2010 - 19:00Used to be good, now the pits!
Anonymous (not verified) on Wed, 09/15/2010 - 14:57iStock - not again, not ever...
Heater (not verified) on Tue, 03/22/2011 - 06:25istockphoto search is no
Alex (not verified) on Mon, 04/04/2011 - 22:18istock search
Steve Gibson on Fri, 04/08/2011 - 04:52I hear you alax, I've already been fairly vocal over the past few years about how the search at istock has been gradually whittled at until its become (as of 2011 for me) unusable. the results are indeed a mine-field of premium priced images that you can't sort by and istock have made it clear that there will be filtering/ordering features to allow sort by price. its a real shame, with all the keywords disambiguated the results should be excellent, and indeed are better than most if it were not for the various ill motived annoyances.
e.g. try a search between shutterstock and istock for "camera book" (i.e. a photo of a book and camera to emote learning or books about cameras etc) at time or writing on SS all you get is a page after page of books with not a photo with a camera in sight, istockphoto at least does show me a photo of a camera sitting on an open book - perfect!
It's only when you use search in earnest that you really see problems arise. Personally iI've stopped buying from IS long ago, SS is only acceptable if you are tied to that subscription otherwise it would be very temptng to go somewhere else, searching images is not easy
Istock files acceptance
Santhosh (not verified) on Sat, 12/03/2011 - 16:19istock change
Steve Gibson on Sun, 12/04/2011 - 22:28istock will change when they have to - but that's not guaranteed. This is only my opinion, but from external appearances istock seems partially paralyzed by what seems like an internal morass of 'big business'. They will either change or suffer some mortification at Getty's hands. No company is too large to fail and the larger they are and the less in touch with customers and contributors they get more likely that is. Once trust has been lost (for many that is already the case) then it's very hard to win back.
BUT... (isn't there always one) the large contributors with bargaining power to create bulk image submissions, bargain for higher royalties etc. can more than supply istock with 'most' of it's fresh image needs, meaning 'they can do this'.
It's interesting to hear this from a newbie(if you are?), most experienced microstockers, tho perhaps upset at times, look at their income from istock and, perhaps begrudgingly continue uploading; things are always changing and falling istock incomes might mean a revaluation for many. For me its the little things that annoy, a seemingly 'well controlled' amount of free speech in the istock forums (bans, locked threads etc) troubles me deeply - and would from any business.